Bug 34440: Enforce lead/trail restrictions

Bug 34440: Enforce lead/trail restrictions

This patch adds rule enforcement into the user interface. When
attempting to make a booking now, instead of just visually displaying
the lead and trail period and highlighting when an overlap appears, we
now block the ability to select a date when such an overlap case is
found.

Sponsored-by: Cuyahoga County Public Library <https://cuyahogalibrary.org/>
Signed-off-by: Kristi Krueger <KKRUEGER@cuyahogalibrary.org>
Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>